If you are a postpaid plan subscriber the settings for mobile data is already provided by globe at the time that they handed you your Samsung Galaxy S3. Cases maybe the signal in your local area does not cover the 3G signal or the setting for the network mode of your smart phone was set to GSM only (Go to settings>wireless network>more settings>mobile networks>network mode to verify). You can check if you have the right setting for the Access Point myGlobe Internet. You can manually configure your settings for that.